Engine exhaust valve stem seal for high temperature and pressure applications

ABSTRACT

An exhaust valve stem seal assembly includes a casing and an elastomeric seal coupled to the casing. The elastomeric seal includes a stem seal portion for sealing against a stem of an exhaust valve. The stem seal portion includes a gas lip that extends radially inward. The casing includes a frustoconical shoulder extending radially inward toward a valve axis to a distal edge. The frustoconical shoulder defines an angle relative to a plane perpendicular to the valve axis between the range of 5° and 45°. The distal edge of the frustoconical shoulder is disposed behind and is substantially aligned with the gas lip along the valve axis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/592,174, filed on Jan. 30, 2012, the disclosureof which is hereby incorporated by reference.

TECHNICAL FIELD

The invention generally relates to an exhaust valve stem seal assemblyfor an internal combustion engine.

BACKGROUND

In some internal combustion engines, a valve guide is positioned withina cylinder head of an internal combustion engine to guide an exhaustvalve in reciprocating motion. The valve guide supports and guides astem of the exhaust valve for axially movement along a valve axis.Clearance is provided between the valve guide and the exhaust valve stemin order to allow free movement between the valve guide and the exhaustvalve stem. A stem seal assembly is coupled to the valve guide and sealsagainst the stem of the exhaust valve to prevent combustion gases fromescaping through the clearance between the exhaust valve stem and thevalve guide. The exhaust valve stem seal assembly further meters oilinto the valve guide to lubricate between the valve stem and the valveguide.

The stem seal assembly is generally comprised of a steel casingsupporting an elastomeric seal. The elastomeric seal expands whensubjected to high temperatures and high exhaust gas pressures. Thisthermal expansion of the elastomeric seal reduces the ability of theelastomeric seal to maintain oil flow to the valve guide, which mayresult in excessive wear of the valve guide.

SUMMARY

A seal assembly for an exhaust valve stem of an engine is provided. Theseal assembly includes a casing having an annular body portion thatextends between a first axial end and a second axial end along a valveaxis. The annular body portion further defines an interior. Anelastomeric seal is coupled to the casing. The elastomeric seal includesa guide seal portion, a stem seal portion, and a shoulder portion. Theguide seal portion is disposed within the interior of the annular bodyportion for engaging a valve guide. The stem seal portion extends awayfrom the casing and the second axial end of the annular body portionalong the valve axis for engaging a valve stem. The shoulder portioninterconnects the guide seal portion and the stem seal portion adjacentthe second axial end of the annular body portion. The stem seal portionincludes a gas lip that extends radially inward toward the valve axisand toward the first axial end of the annular body portion. A void isdefined between the gas lip and the shoulder portion of the elastomericseal. The casing includes a frustoconical shoulder extending from thesecond axial end of the annular body portion to a distal edge of thefrustoconical shoulder. The frustoconical shoulder extends radiallyinward toward the valve axis and away from the first axial end of theannular body portion.

An exhaust valve stem seal assembly for an engine is provided. Theexhaust valve stem seal assembly includes a casing having an annularbody portion extending between a first axial end and a second axial endalong a valve axis. The annular body portion defines an interior. Anelastomeric seal is coupled to the casing. The elastomeric seal includesa guide seal portion, a stem seal portion and a shoulder portion. Theguide seal portion is disposed within the interior of the annular bodyportion for engaging a valve guide. The stem seal portion extends awayfrom the casing and the second axial end of the annular body portionalong the valve axis for engaging a valve stem. The shoulder portioninterconnects the guide seal portion and the stem seal portion. The stemseal portion includes a gas lip that extends radially inward toward thevalve axis and toward the first axial end of the annular body portion. Avoid is defined between the gas lip and the shoulder portion of theelastomeric seal. The casing includes a frustoconical shoulder thatextends from the second axial end of the annular body portion to adistal edge. The frustoconical shoulder extends radially inward towardthe valve axis and away from the first axial end of the annular bodyportion to the distal edge. The distal edge of the frustoconicalshoulder is substantially aligned with the gas lip along the valve axis.The frustoconical shoulder defines an angle relative to a plane that isperpendicular to the valve axis between the range of 5° and 45°.

Accordingly, the frustoconical shoulder of the casing angles from theannular body portion of the casing toward the gas lip, and extends fromthe second axial end of the annular body portion to the distal edge ofthe frustoconical shoulder, which is located immediately behind the gaslip. As such, as the stem seal portion of the elastomeric seal expandsin response to high temperatures and high pressure, the distal edge ofthe frustoconical shoulder acts as a hinge or pivot point to allow thestem seal portion of the elastomeric seal to expand and rotate away fromthe stem of the exhaust valve, thereby maintaining the proper shape andconfiguration of the gas lip and preventing the void located behind thegas lip from collapsing. By maintaining the proper shape andconfiguration of the gas lip, and by preventing the void fromcollapsing, lubricating oil may be properly metered past the gas lipinto the clearance between the valve guide and the exhaust valve stemfor lubrication therebetween.

The above features and advantages and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic partial cross sectional view of an exhaust valvestem seal assembly sealing against a valve stem supported by a valveguide.

FIG. 2 is a schematic cross sectional view of the exhaust valve stemseal assembly.

FIG. 3 is a schematic enlarged fragmentary cross sectional view of theexhaust valve stem seal.

DETAILED DESCRIPTION

Those having ordinary skill in the art will recognize that terms such as“above,” “below,” “upward,” “downward,” “top,” “bottom,” etc., are useddescriptively for the figures, and do not represent limitations on thescope of the invention, as defined by the appended claims.

Referring to the Figures, wherein like numerals indicate like partsthroughout the several views, a seal assembly is generally shown at 20.The seal assembly 20 may be referred to as an exhaust valve stem sealassembly 20.

Referring to FIG. 1, a valve guide 22 is disposed within a bore 23 of acylinder head 24. The valve guide 22 defines a central bore 25 thatslideably supports a stem 26 of an exhaust valve 28 for reciprocatingmovement along a valve axis 30. The valve axis 30 is located along alongitudinal center of the stem 26. The seal assembly 20 is coupled orattached to the valve guide 22.

Referring also to FIGS. 2 and 3, the seal assembly 20 includes a casing32 supporting an elastomeric seal 34. The casing 32 includes an annularbody portion 36 that extends along the valve axis 30 between a firstaxial end 38 and a second axial end 40 of the annular body portion 36.The annular body portion 36 includes a generally tubular shape anddefines an interior 42. The casing 32 includes a frustoconical shoulder44 that extends from the second axial end 40 of the annular body portion36 to a distal edge 46. The frustoconical shoulder 44 extends radiallyinward toward the valve axis 30, and also extends away from the firstaxial end 38 of the annular body portion 36 to the distal edge 46. Thefrustoconical shoulder 44 includes a frustoconical shape generallydefined as a cone shape with the tip of the cone removed. While thefrustoconical shoulder 44 is shown to include a planar cross section, itshould be appreciated that the frustoconical shoulder 44 mayalternatively include a slightly curved cross sectional shape, such asbut not limited to a slightly convex cross sectional shape. A flange 48extends radially outward from the first axial end 38 of the annular bodyportion 36, away from the valve axis 30.

Referring to FIG. 3, the cross section of the frustoconical shoulder 44is substantially disposed along a plane 49. The plane 49 is disposedrelative to a plane 50, which is perpendicular to the valve axis 30, todefine an angle 52 therebetween. The angle 52 between the plane 49 ofthe frustoconical shoulder 44 and the plane 50 is preferably between therange of 5° and 45°. The casing 32 may include and be manufactured froma metal, such as but not limited to steel. However, the casing 32 may bemanufactured from some other suitable material.

The elastomeric seal 34 is coupled to the casing 32. The elastomericseal 34 includes and is manufactured from an elastomer suitable forsealing against the valve guide 22 and the stem 26 of the exhaust valve28 in a high temperature and high pressure environment. The elastomericseal 34 includes a guide seal portion 54, a stem seal portion 56, and ashoulder portion 58. The guide seal portion 54 is disposed within theinterior 42 of the annular body portion 36 of the casing 32. The guideseal portion 54 engages the valve guide 22 in sealing/frictionalengagement therewith. The stem seal portion 56 extends away from thecasing 32 and the second axial end 40 of the annular body portion 36,along the valve axis 30. Accordingly, the stem seal portion 56 extendsfrom the second axial end 40 of the annular body portion 36 in adirection opposite the first axial end 38 of the annular body portion36. Accordingly, the stem seal portion 56 is not radially constrainedabout the valve axis 30 by the casing 32, thereby allowing the stem sealportion 56 to expand radially in response to increased temperature andpressure. As shown, a garter spring clip 60 is disposed within a groove62 defined by the stem seal portion 56 of the elastomeric seal 34 toradially bias the stem seal portion 56 against the stem 26 of theexhaust valve 28. The stem seal portion 56 engages the stem 26 of theexhaust valve 28 in sealing engagement therewith. The shoulder portion58 interconnects the guide seal portion 54 and the stem seal portion 56,and is disposed adjacent the second axial end 40 of the annular bodyportion 36 of the casing 32.

As best shown in FIG. 3, the stem seal portion 56 includes a gas lip 64.The gas lip 64 seals against the stem 26 of the exhaust valve 28 toprevent gases from escaping through the interface between the valveguide 22 and the stem 26 of the exhaust valve 28. While the gas lip 64prevents gases from escaping in a direction indicated by arrow 66, thegas lip 64 allows lubricating oil to pass in a direction opposite arrow66, to lubricate the interface between the valve guide 22 and the stem26 of the exhaust valve 28. The gas lip 64 extends radially inwardtoward the valve axis 30, and extends toward the first axial end 38 ofthe annular body portion 36. The gas lip 64 is spaced from the shoulderportion 58 of the elastomeric seal 34 to define a void 68 between thegas lip 64 and the shoulder portion 58.

As best shown in FIG. 3, the distal edge 46 of the frustoconicalshoulder 44 is positioned to substantially align with the gas lip 64along the valve axis 30. In other words, the distal edge 46 of thefrustoconical shoulder 44 is disposed radially outward of the gas lip64, and is disposed at approximately the same axial location along thevalve axis 30 as the gas lip 64. Preferably, the distal edge 46 of thefrustoconical shoulder 44 is within an axial distance of the gas lip 64measured along the valve axis 30. The axial distance is equal to twice adistance 76 between a bottom or lower edge 78 of the gas lip 64 and atop or upper edge 80 of the void 68 as measured along the valve axis 30.Preferably, but not necessarily, the lower surface 82 of the distal edge46 of the frustoconical shoulder 44 is spaced from the first axial end38 of the annular body a distance 70 that is equal to or less than,within acceptable manufacturing tolerances, a distance 72 between alower edge 84 of a base of the gas lip 64 and the first axial end 38 ofthe annular body. The base of the gas lip 64 is the general location atwhich the gas lip 64 is attached to and extends from the stem sealportion 56, and is generally indicated by the dashed line 74.

By positioning the gas lip 64 at the approximate same axial locationalong the valve axis 30 as the distal edge 46 of the frustoconicalshoulder 44, the distal edge 46 acts as a hinge or pivot to allow thestem seal portion 56 to rotate upward and away from the casing 32. Morespecifically, the frustoconical shoulder 44 allows the stem seal portion56 of the elastomeric seal 34 to rotate radially outward away from thevalve axis 30 and axially away from the first axial end 38 of theannular body portion 36 of the casing 32 in response to thermalexpansion of the elastomeric seal 34. Allowing the stem seal portion 56to rotate in this fashion maintains a substantially constant pressureand contact width between the gas lip 64 and the stem 26 of the exhaustvalve 28, which maintains proper functionality of the gas lip 64 in hightemperature and high pressure environments.

The detailed description and the drawings or figures are supportive anddescriptive of the invention, but the scope of the invention is definedsolely by the claims. While some of the best modes and other embodimentsfor carrying out the claimed invention have been described in detail,various alternative designs and embodiments exist for practicing theinvention defined in the appended claims.

1. A seal assembly for an exhaust valve stem of an engine, the sealassembly comprising: a casing having an annular body portion extendingbetween a first axial end and a second axial end along a valve axis, anddefining an interior; an elastomeric seal coupled to the casing andincluding a guide seal portion disposed within the interior of theannular body portion for engaging a valve guide, a stem seal portionextending away from the casing and the second axial end of the annularbody portion along the valve axis for engaging a valve stem, and ashoulder portion interconnecting the guide seal portion and the stemseal portion; wherein the stem seal portion includes a gas lip extendingradially inward toward the valve axis and toward the first axial end ofthe annular body portion, and defines a void between the gas lip and theshoulder portion of the elastomeric seal; and wherein the casingincludes a frustoconical shoulder extending from the second axial end ofthe annular body portion radially inward toward the valve axis and awayfrom the first axial end of the annular body portion to a distal edge.2. A seal assembly as set forth in claim 1 wherein the distal edge ofthe frustoconical shoulder is substantially aligned with the gas lipalong the valve axis.
 3. A seal assembly as set forth in claim 2 whereinthe distal edge of the frustoconical shoulder is within an axialdistance of the gas lip along the valve axis, and wherein the axialdistance is equal to twice a distance between a lower edge of the gaslip and an upper edge of the void as measured along the valve axis.
 4. Aseal assembly as set forth in claim 1 wherein a cross section of thefrustoconical shoulder is substantially disposed along a plane, andwherein the plane of the cross section of the frustoconical shoulderdefines an angle relative to a plane perpendicular to the valve axisbetween the range of 5° and 45°.
 5. A seal assembly as set forth inclaim 1 wherein the frustoconical shoulder is configured to allow thestem seal portion of the elastomeric seal to rotate radially outwardaway from the valve axis and axially away from the first axial end ofthe annular body portion of the casing to maintain a substantiallyconstant pressure and contact width between the gas lip and the valvestem in response to thermal expansion of the elastomeric seal.
 6. A sealassembly as set forth in claim 1 wherein the distal edge of thefrustoconical shoulder is spaced from the first axial end of the annularbody a distance equal to or less than a distance between a base of thegas lip and the first axial end of the annular body.
 7. A seal assemblyas set forth in claim 1 wherein the casing includes and is manufacturedfrom a metal.
 8. A seal assembly as set forth in claim 1 wherein theelastomeric seal includes and is manufactured from an elastomer.
 9. Anexhaust valve stem seal assembly for an engine, the exhaust valve stemseal assembly comprising: a casing having an annular body portionextending between a first axial end and a second axial end along a valveaxis, and defining an interior; an elastomeric seal coupled to thecasing and including a guide seal portion disposed within the interiorof the annular body portion for engaging a valve guide, a stem sealportion extending away from the casing and the second axial end of theannular body portion along the valve axis for engaging a valve stem, anda shoulder portion interconnecting the guide seal portion and the stemseal portion; wherein the stem seal portion includes a gas lip extendingradially inward toward the valve axis and toward the first axial end ofthe annular body portion, and defines a void between the gas lip and theshoulder portion of the elastomeric seal; wherein the casing includes afrustoconical shoulder extending from the second axial end of theannular body portion radially inward toward the valve axis and away fromthe first axial end of the annular body portion to a distal edge;wherein the distal edge of the frustoconical shoulder is substantiallyaligned with the gas lip along the valve axis; and wherein thefrustoconical shoulder defines an angle relative to a planeperpendicular to the valve axis between the range of 5° and 45°.
 10. Anexhaust valve stem seal assembly as set forth in claim 9 wherein thedistal edge of the frustoconical shoulder is within an axial distance ofthe gas lip along the valve axis, and wherein the axial distance isequal to twice a distance between a lower edge of the gas lip and anupper edge of the void as measured along the valve axis.
 11. An exhaustvalve stem seal assembly as set forth in claim 10 wherein thefrustoconical shoulder is configured to allow the stem seal portion ofthe elastomeric seal to rotate radially outward away from the valve axisand axially away from the first axial end of the annular body portion ofthe casing to maintain a substantially constant pressure and contactwidth between the gas lip and the valve stem in response to thermalexpansion of the elastomeric seal.